Method of preparing short-fiber cellulosic material for chemical treatment



Patented Sept. 2, 1924.

UNITED STATES I 1,507,330- PATENT OFFICE.

ALFRED I4. BROADBENT, OF WILMINGTON, DELAWARE, ASSIGNOR TO E. I. DU IEONT DE NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION DELAWARE METHOD OF PREPARING SHORT-FIBER CELLULOSIC MATERIAL FOR CHEMICAL TREATMENT. I

, llo Drawing.

amenable to a Chemical treatment designed.

' l to convert it into certain of its derivatives;

while not restricted thereto the invention is particularly applicable to the preparation of wood pulp for nitration, and therefore I describe it with particular reference to that art.

In order to obtain a uniformly nitrated 2 nitrocellulose from any fibrous material, it is essential that the material be in such physical condition that the nitrating acids will completely penetrate the individual fibers. If the fibrous 'material contains hard com- 2 pact lumps, or is otherwise incompletely opened up, the nitrating acid has to penetrate these hard lumps and the like, instead of having easy and immediate access to all the fibers, and as it penetrates the lumps, the acid becomes gradually weaker in nitric acid as this acid is used up in nitration. The weakened acid that penetrates to the interior of the lumphas a marked hydrolyzing action a on the cellulose, and therefore leads to the production of nitrated compounds of obscure composition which differ from nitrocellulose in being gelatinous in nature, and which exhibit chemical and physical characteristics different from those of true nitrocellulose. If the lumps are exceedingly compact, some of the fiber may even resist nitration entire- 1 The result of using material containing these lumps is the production of nitrated material which is non-uniformly nitrated to 45. such an extent as to be decidedly inferior, or indeed unsuitable, for use for purposes'of colloidization or solution.

The difficulty in obtaining the fibers opened u sufliciently to permit the nitrating acid to reely and uniformly penetrate the individual fibers is especially characteristic of wood pulp. If dried in bulk, the dried niteness and brevity describe it with more 8 fiber cotton in intimate mixture with the Application fileiNovember 8, 1919. Serial No. 335,719.

pulp will contain hard, compact lumps 'of .fiber which cannot be readily opened up to a condition in which the nitrating acid will freely penetrate them. In sheet form, also, wood pulp exhibits a tendency to dry in a condition that prevents the uniform penetration of the nitrating acid. A further objection to theuseof wood pulp for nitration lies in the tendency of the fiber, owing to its shortness, to be carried along in excessive amounts with the spent acid recovered from the nitrating operation whereby the entrained pulp'causes the rapid filling up, of the spent acid filters, and entails other operating difliculties; entrained pulp also occasions losses in the washing processes in the purification treatment subsequent to nitration.

I have devised a method of so preparing short-fiber cellulosic material that the resulting material will not dry in lumps, but on the contrary, after picking will dry to a fluffy form free from hard lumps and of such character that the nitrating acid will readily and uniformly penetrate the individual fibers, thereby yielding a uniformly nitrated nitrocellulose.

In general my nvention consists in the matters hereinafter described and claimed. it being understood that I do not restrict it either to the art of nitration or to the treatment of wood pulp, but for the sake of defiparticular reference to the art of nitrating wood pulp.

-My invention comprises blending wood pulp, which has a relatively short fiber, with cotton in any unspun form, the cotton having a relatively longer fiber than the wood pulp, this blending being done previous to the operations of teasing or picking and drying which precedenitration. The longer short-fiber wood pulp prevents the drying of the wood pulp into hard compact lumps and gives a mixture that, after passing through a teasing or picking machine, will dry to a flufl'y formfree from hard lumps, with the fiber opened up sufliciently to permit the nitrating acid to freely and uniformly penetrate all the individual fibers, so that, upon nitration, a. superior and uniformly nitrated nitrocellulose is produced. Also, the various giving, as before stated, a fluffy form free .difiiculties that would ordinarily bemet with, and losses that would ordinarily be sustained because of the tendency of wood pulp to penetrate the holes in the apparatus used in the nitrating and purifying operations, are greatly. minimized. v

In proceeding in accordance with my in- I vention, I prefer to use a mixture of equal parts of cotton fiber andwood pulp, but can secure the desired results with as low as forty per cent cotton fiber tosixty per cent wood pulp. Of course, mixtures having a larger percentage'of cotton fiber can be used if desired. There is no restriction as to the particular grades of cotton fiber which can be used. I have found, however, that the most satisfactory results are obtained either with cotton linters, or with a mixture of cot- .ton linters with another or other grades of cotton fiber in which mixture the amount of cotton lintersis at least fifty per cent of the total amount of cotton fiber present. The

nitrocellulose resulting from the nitration of cottonis in no way objectionable for the To obtain the desired uniformity in the mixture, itis necessary to thoroughly separate the'fibers of the wood pulp, preferably by'steeping in water. be charged with the crude. cotton into a digestor and submitted to the purification treatment accorded to the cotton, or it may be added to the cotton at any subsequent operation as in the bleaching or washing operations, provided there is agitation sufficient to intimately blend the two materials.

0 After squeezing out the bulk of the water from the mixture of wood pulp and cotton, and passing the material through a teasing or picking machine, the; mixture is dried,

from hard lumps and so forth. The material so prepared may then be nitrated in any usual or preferred way.

Having thus described my invention, I

claim: H

1. In the conversion of short-fiber cellulosic material into esters thereof, the method which comprises mixing with such material 4. In the nitration of wood 'pulp, the

method which comprises'mixing CO'CtOIlfibGI with the wood-pulp.

5. In the nitration of wood pulp, the method which comprises mixing with the ,wood pulp substantially an equal of cotton fiber.

quantity '6. In the conversion of short-fiber cellulosic material into esters thereof, the method which comprises adding to the material a cellulosic longer-fiber material, agitating materials with liquid thereby to intimately,

The wood pulp may, mixythem, removing the bulk of the liquid.

ture.

L. BROADBENT.

the, 

